Tosfos in a few places implies that to be chayav for ta'am k'ikur, there still needs to be a full shiur of the isur, the chidush being that even though it is completely absorbed one is still chayav - (36B d"h Ukzayis at the end "shehivlia k'zayis yayin"; and 37A d"h V'chi Taima where it is suggested that even when there is a k'zayis of yayin it is still ta'am k'ikur"). Is this a correct understanding of Tosfos? Rivan explains the din of ta'am k'ikur (37A D'H Dilma) as when one soaked grapes in water, where it would not appear that a full shiur of isur was absorbed. And the gemora talks about the case of giulei nachrim as being ta'am k'ikur. It is hard to imagine that a full shiur of isur is transferred in and out of the pot. So why does Tosfos talk about a complete shiur of a k'zayis of isur for ta'am k'ikur in these places? Thank you!
YZ Friedman, Toronto, Canada
This is a strong question. Let's take it apart and answer it piece by piece, bs'd.
1) You ask, "Tosfos... implies that... for Ta'am k'Ikar, there still needs to be a full Shi'ur of the Isur." Your first supporting proof is Tosfos 36b, DH uk'Zayis, "at the end, 'she'Hivli'a k'Zayis Yayin." Note that Tosfos says, "Hashta Sevira Lei l'Abaye," meaning that this is a transient conception of the Din, and merely a stage of logical dissection. This understanding does not remain true in the conclusion.
2) Your second supporting proof is Tosfos 37a, DH v'Chi Teima, "where it is suggested that even when there is a k'Zayis of Yayin it is still Ta'am k'Ikar." Here also, this is not a final conclusion. Take a look at Tosfos DH v'Yesh, where Tosfos says "Hayah Savur," indicating that this is not the final word in this Sugya. You are correct in pointing out that at this juncture we are talking about a special Isur of Nezirus -- a full Shi'ur which was absorbed in bread. Since the wine was absorbed, we cannot consider the wine by itself to be a k'Zayis; we must consider its Shi'ur together with the bread which absorbed it. On this the Gemara asks, "What is the Chidush?" This case is no less serious than "Ta'am K'Ikar," which is Asur in all of the Isurim in the Torah, not just in Isurei Nazir.
3) As a result, we see that your understanding of "Ta'am K'ikar" is 100% correct, that it is only Ta'am and not a Shi'ur of Isur, and that is why Gi'ulei NOchrim is Asur with Ta'am alone and no Shi'ur. The seeming contradictions to this understanding were preliminary stages of clarification.
4) According to Rashi and the Rambam, the above Isur of only Ta'am is d'Rabanan, and that Ta'am k'Ikar is only Asur mid'Oraisa where you have a k'Zayis in a Kedei Achilas Pras. However, Tosfos holds that even if there is only Ta'am, it is an Isur d'Oraisa (and his primary proof is from Gi'ulei Nochrim). For a comprehensive and concise explanation of Ta'am k'Ikar, see the Aruch ha'Shulchan YD 98.
Shimon Brodie